U.S. patent application number 17/137516 was filed with the patent office on 2022-06-30 for fountain solution thickness measurement using optical properties of solidified fountain solution in a lithography printing system.
The applicant listed for this patent is Xerox Corporation. Invention is credited to Douglas K. HERRMANN, Jason M. LEFEVRE, Michael J. LEVY, Chu-heng LIU, Paul J. MCCONVILLE, Seemit PRAHARAJ.
Application Number | 20220203749 17/137516 |
Document ID | / |
Family ID | |
Filed Date | 2022-06-30 |
United States Patent
Application |
20220203749 |
Kind Code |
A1 |
HERRMANN; Douglas K. ; et
al. |
June 30, 2022 |
FOUNTAIN SOLUTION THICKNESS MEASUREMENT USING OPTICAL PROPERTIES OF
SOLIDIFIED FOUNTAIN SOLUTION IN A LITHOGRAPHY PRINTING SYSTEM
Abstract
According to aspects of the embodiments, there is provided a
method of measuring the amount of fountain solution employed in a
digital offset lithography printing system. Fountain solution
thickness is measured using a glass roll at a lower temperature
than the fountain solution. The lower temperature causes the
fountain solution to undergo a change in state and in a solid state
the fountain solution crystalizes and changes roll opacity with the
thickness of the film. When radiated with a light source the
opacity is continuously measured through the surface of the roller.
The thickness of the crystallized fountain solution can then be
determined via the opacity level increase by the crystallization
and the impact to the opacity on the glass roll.
Inventors: |
HERRMANN; Douglas K.;
(Webster, NY) ; LIU; Chu-heng; (Penfield, NY)
; PRAHARAJ; Seemit; (Webster, NY) ; MCCONVILLE;
Paul J.; (Webster, NY) ; LEFEVRE; Jason M.;
(Penfield, NY) ; LEVY; Michael J.; (Webster,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Xerox Corporation |
Norwalk |
CT |
US |
|
|
Appl. No.: |
17/137516 |
Filed: |
December 30, 2020 |
International
Class: |
B41N 3/08 20060101
B41N003/08; B41F 33/00 20060101 B41F033/00; B41F 7/24 20060101
B41F007/24 |
Claims
1. A method to measure fountain solution thickness for variable
data lithography printing comprising: transferring fountain
solution from an imaging member onto an engineered surface by
evaporating the fountain solution on the imaging member and
re-condensing on the engineered surface, the engineered surface
having an opacity that varies as a function of fountain solution
thickness; using an emissive light source to pass a light along a
path from the source through the engineered surface; receiving
light passing through the engineered surface at a light detector;
generating a signal proportional to the opacity level of the
engineered surface from the light impinging on the light detector;
and determining the thickness of the fountain solution on the
engineered surface from the opacity level.
2. A method to measure fountain solution thickness for variable
data lithography printing comprising: using an engineered surface
with an opacity that varies as a function of fountain solution
thickness, using an emissive light source to pass a light along a
path from the source through the engineered surface, receiving
light passing through the engineered surface at a light detector;
generating a signal proportional to the opacity level of the
engineered surface from the light impinging on the light detector;
and determining the thickness of the fountain solution on the
engineered surface from the capacity level, the method further
comprising cooling the engineered surface to phase change the
fountain solution to a solid.
3. The method in accordance to 1, wherein the light source and the
light detector are positioned on respective opposite portions of
the engineered surface.
4. The method according to claim 3, wherein the light detector
records the light transmitted through the engineered surface.
5. The method according to claim 4, wherein the engineered surface
is a clear glass roll.
6. The method according to claim 5, wherein the emissive light
source is contained within the clear glass roll.
7. The method in accordance to claim 4, the method further
comprising: applying a layer of fountain solution to an imaging
member having an arbitrarily reimageable imaging surface.
8. The method in accordance to claim 7, the method further
comprising: transferring a portion of the fountain solution on the
imaging member onto the engineered surface.
9. The method in accordance to claim 8, wherein the transferring
includes evaporating the fountain solution on the imaging member
and deposition the engineered surface.
10. The method according to claim 9, wherein the determining the
thickness of the fountain solution is evaluating an image for solid
texture to evaluate opacity and thickness via image analysis.
11. An ink-based digital printing system useful for ink printing,
comprising: a processor; and a storage device coupled to the
processor, wherein the storage device comprises instructions which,
when executed by the processor, cause the processor to control
fountain solution deposition process and maintain fountain solution
at a set thickness for variable data lithography printing by: using
an engineered surface with an opacity that varies as a function of
fountain solution thickness; using an emissive light source to pass
a light along a path from the source through the engineered
surface; receiving light passing through the engineered surface at
a light detector; generating a signal proportional to the opacity
level of the engineered surface from the light impinging on the
light detector; determining the thickness of the fountain solution
on the engineered surface from the opacity level; and controlling
the fountain solution deposition process based on the determined
thickness of the fountain solution, the process further performing
cooling the engineered surface to phase change the fountain
solution to a solid.
12. (canceled)
13. The ink-based digital printing system in accordance to 11,
wherein the light source and the light detector are positioned on
respective opposite portions of the engineered surface.
14. The ink-based digital printing system according to claim 13,
wherein the light detector records the light transmitted through
the engineered surface.
15. The ink-based digital printing system according to claim 14,
wherein the engineered surface is a clear glass roll.
16. The ink-based digital printing system according to claim 15,
wherein the emissive light source is contained within the clear
glass roll.
17. The ink-based digital printing system in accordance to claim
13, the processor further performing: applying a layer of fountain
solution to an imaging member having an arbitrarily reimageable
imaging surface.
18. The ink-based digital printing system in accordance to claim
17, the processor further performing: transferring a portion of the
fountain solution on the imaging member onto the engineered
surface.
19. The ink-based digital printing system in accordance to claim
18, wherein the transferring is evaporating the fountain solution
on the imaging member and re-condensing on the engineered
surface.
20. The ink-based digital printing system according to claim 19,
wherein the determining the thickness of the fountain solution is
evaluating an image for solid texture to evaluate opacity and
thickness via image analysis.
21. The method in accordance to 1, further comprising controlling
the fountain solution deposition process based on the determined
thickness of the fountain solution.
Description
FIELD OF DISCLOSURE
[0001] This invention relates generally to digital printing
systems, and more particularly, to fountain solution deposition
systems and methods for measuring the thickness of the fountain
solution.
BACKGROUND
[0002] Conventional lithographic printing techniques cannot
accommodate true high speed variable data printing processes in
which images to be printed change from impression to impression,
for example, as enabled by digital printing systems. The
lithography process is often relied upon, however, because it
provides very high quality printing due to the quality and color
gamut of the inks used. Lithographic inks are also less expensive
than other inks, toners, and many other types of printing or
marking materials.
[0003] Ink-based digital printing uses a variable data lithography
printing system, or digital offset printing system, or a digital
advanced lithography imaging system. A "variable data lithography
system" is a system that is configured for lithographic printing
using lithographic inks and based on digital image data, which may
be variable from one image to the next. "Variable data lithography
printing," or "digital ink-based printing," or "digital offset
printing," or digital advanced lithography imaging is lithographic
printing of variable image data for producing images on a substrate
that are changeable with each subsequent rendering of an image on
the substrate in an image forming process.
[0004] For example, a digital offset printing process may include
transferring ink onto a portion of an imaging member (e.g.,
fluorosilicone-containing imaging member, imaging blanket, printing
plate) that has been selectively coated with a fountain solution
(e.g., dampening fluid) layer according to variable image data.
According to a lithographic technique, referred to as variable data
lithography, a non-patterned reimageable surface of the imaging
member is initially uniformly coated with the fountain solution
layer. An imaging system then evaporates regions of the fountain
solution layer in an image area by exposure to a focused radiation
source (e.g., a laser light source, high power laser) to form
pockets. A temporary pattern latent image in the fountain solution
is thereby formed on the surface of the digital offset imaging
member. The latent image corresponds to a pattern of the applied
fountain solution that is left over after evaporation. Ink applied
thereover is retained in the pockets where the laser has vaporized
the fountain solution. Conversely, ink is rejected by the plate
regions where fountain solution remains. The inked surface is then
brought into contact with a substrate at a transfer nip and the ink
transfers from the pockets in the fountain solution layer to the
substrate. The fountain solution may then be removed, a new uniform
layer of fountain solution applied to the printing plate, and the
process repeated.
[0005] Digital printing is generally understood to refer to systems
and methods of variable data lithography, in which images may be
varied among consecutively printed images or pages. "Variable data
lithography printing," or "ink-based digital printing," or "digital
offset printing" are terms generally referring to printing of
variable image data for producing images on a plurality of image
receiving media substrates, the images being changeable with each
subsequent rendering of an image on an image receiving media
substrate in an image forming process. "Variable data lithographic
printing" includes offset printing of ink images generally using
specially-formulated lithographic inks, the images being based on
digital image data that may vary from image to image, such as, for
example, between cycles of an imaging member having a reimageable
surface.
[0006] The inventors have found that the amount or thickness of the
fountain layer which is present on the printing plate is a critical
part of digital offset printing methods in order to maintain sharp
and clear images. The layer is extremely thin, on the order of tens
of nanometers, which until now any direct measurement of its
thickness difficult. Knowledge of the layer thickness is helpful to
control the system image quality. For example, if insufficient
fountain solution is provided to a non-image area, the ink will
invade the non-image area to create a distorted printing image.
Conversely, if too much fountain solution is provided so that the
fountain solution enters the image area, a distortion of the image
will also result.
[0007] The amount or thickness of fountain solution which is
applied to the printing plates is therefore critical to the
production of clear printed images. Currently, the amount of
fountain solution which is applied to the plates used in offset
lithography is based principally on the experience of the offset
press operator. There is to date no accurate method of quantifying
the amount of fountain solution used in offset lithography printing
processes so as to minimize the undesirable effects of too much or
too little fountain solution.
[0008] It would therefore be a significant advance in the art of
digital offset printing if the amount of fountain solution which is
used in the marking process could be quantified without disrupting
the operation of the printing process.
SUMMARY
[0009] The following presents a simplified summary in order to
provide a basic understanding of some aspects of one or more
embodiments or examples of the present teachings. This summary is
not an extensive overview, nor is it intended to identify key or
critical elements of the present teachings, nor to delineate the
scope of the disclosure. Rather, its primary purpose is merely to
present one or more concepts in simplified form as a prelude to the
detailed description presented later. Additional goals and
advantages will become more evident in the description of the
figures, the detailed description of the disclosure, and the
claims.
[0010] The foregoing and/or other aspects and utilities embodied in
the present disclosure may be achieved by providing a fountain
solution thickness measurement system. The measurement system for
thin liquid film, such as fountain solution, uses optical
properties of a phase changed film to determine the thickness of
the fountain solution.
[0011] The propose fountain solution thickness measurement system
using optical properties of solidified fountain solution film. It
is further proposed to transfer a concentration of the fountain
solution from an imaging blanket to a clear or glass roller with an
engineered surface of known surface roughness. Further, the
fountain solution layer is evaporated or frozen into a solid state
that can then be measured for opacity by an emissive light source
and sensor.
[0012] According to aspects illustrated herein, an exemplary method
to measure fountain solution thickness for variable data
lithography printing comprising using an engineered surface with an
opacity that varies as a function of fountain solution thickness;
using an emissive light source to pass a light along a path from
the source through the engineered surface; receiving light passing
through the engineered surface at a light detector; generating a
signal proportional to the opacity level of the engineered surface
from the light impinging on the light detector; and determining the
thickness of the fountain solution on the engineered surface from
the opacity level.
[0013] According to aspects described herein, a system useful for
printing with an ink-based digital image forming device comprising
a processor; and a storage device coupled to the processor, wherein
the storage device comprises instructions which, when executed by
the processor, cause the processor to control fountain solution
deposition process maintain fountain solution at a set thickness
for variable data lithography printing by: using an engineered
surface with an opacity that varies as a function of fountain
solution thickness; using an emissive light source to pass a light
along a path from the source through the engineered surface;
receiving light passing through the engineered surface at a light
detector; generating a signal proportional to the opacity level of
the engineered surface from the light impinging on the light
detector; determining the thickness of the fountain solution on the
engineered surface from the opacity level; and controlling the
fountain solution deposition process based on the determined
thickness of the fountain solution.
[0014] Exemplary embodiments are described herein. It is
envisioned, however, that any system that incorporates features of
apparatus and systems described herein are encompassed by the scope
and spirit of the exemplary embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Various exemplary embodiments of the disclosed apparatuses,
mechanisms and methods will be described, in detail, with reference
to the following drawings, in which like referenced numerals
designate similar or identical elements, and:
[0016] FIG. 1 is block diagram of a digital image forming device in
accordance with examples of the embodiments;
[0017] FIG. 2 shows a schematic view of a clear glass roll with
internal emissive lighting system to illuminate solidified fountain
solution on surface of roller in accordance to an embodiment;
[0018] FIG. 3 is part of a digital image forming device that
includes a feedback loop for controlling and applicator that
dispenses fluid solution in accordance to an embodiment;
[0019] FIG. 4 is a block diagram of a controller with a processor
for executing instructions to automatically control devices in the
digital image forming device depicted in FIGS. 1-3 in accordance to
an embodiment;
[0020] FIG. 5 shows transferring fountain solution by evaporation
from the imaging blanket to the clear glass roll for fountain
solution measurement in accordance to an embodiment;
[0021] FIG. 6 is a plot of opacity as a function of thickness of
the solidified fountain solution in accordance to an embodiment;
and
[0022] FIG. 7 is a flowchart depicting the operation of an
exemplary method to directly measure fountain solution for use in a
digital image forming device.
DETAILED DESCRIPTION
[0023] Illustrative examples of the devices, systems, and methods
disclosed herein are provided below. An embodiment of the devices,
systems, and methods may include any one or more, and any
combination of, the examples described below. This invention may,
however, be embodied in many different forms and should not be
construed as limited to the embodiments set forth below. Rather,
these exemplary embodiments are provided so that this disclosure
will be thorough and complete, and will fully convey the scope of
the invention to those skilled in the art. Accordingly, the
exemplary embodiments are intended to cover all alternatives,
modifications, and equivalents as may be included within the spirit
and scope of the apparatuses, mechanisms and methods as described
herein.
[0024] We initially point out that description of well-known
starting materials, processing techniques, components, equipment
and other well-known details may merely be summarized or are
omitted so as not to unnecessarily obscure the details of the
present disclosure. Thus, where details are otherwise well known,
we leave it to the application of the present disclosure to suggest
or dictate choices relating to those details. The drawings depict
various examples related to embodiments of illustrative methods,
apparatus, and systems for inking from an inking member to the
reimageable surface of a digital imaging member.
[0025] When referring to any numerical range of values herein, such
ranges are understood to include each and every number and/or
fraction between the stated range minimum and maximum. For example,
a range of 0.5-6% would expressly include the endpoints 0.5% and
6%, plus all intermediate values of 0.6%, 0.7%, and 0.9%, all the
way up to and including 5.95%, 5.97%, and 5.99%. The same applies
to each other numerical property and/or elemental range set forth
herein, unless the context clearly dictates otherwise.
[0026] The modifier "about" used in connection with a quantity is
inclusive of the stated value and has the meaning dictated by the
context (for example, it includes at least the degree of error
associated with the measurement of the particular quantity). When
used with a specific value, it should also be considered as
disclosing that value. For example, the term "about 2" also
discloses the value "2" and the range "from about 2 to about 4"
also discloses the range "from 2 to 4."
[0027] The term "controller" is used herein generally to describe
various apparatus such as a computing device relating to the
operation of one or more device that directs or regulates a process
or machine. A controller can be implemented in numerous ways (e.g.,
such as with dedicated hardware) to perform various functions
discussed herein. A "processor" is one example of a controller
which employs one or more microprocessors that may be programmed
using software (e.g., microcode) to perform various functions
discussed herein. A controller may be implemented with or without
employing a processor, and also may be implemented as a combination
of dedicated hardware to perform some functions and a processor
(e.g., one or more programmed microprocessors and associated
circuitry) to perform other functions. Examples of controller
components that may be employed in various embodiments of the
present disclosure include, but are not limited to, conventional
microprocessors, application specific integrated circuits (ASICs),
and field-programmable gate arrays (FPGAs).
[0028] The terms "media", "print media", "print substrate" and
"print sheet" generally refers to a usually flexible physical sheet
of paper, polymer, Mylar material, plastic, or other suitable
physical print media substrate, sheets, webs, etc., for images,
whether precut or web fed. The listed terms "media", "print media",
"print substrate" and "print sheet" may also include woven fabrics,
non-woven fabrics, metal films, and foils, as readily understood by
a skilled artisan.
[0029] The term "image forming device", "printing device" or
"printing system" as used herein may refer to a digital copier or
printer, scanner, image printing machine, xerographic device,
electrostatographic device, digital production press, document
processing system, image reproduction machine, bookmaking machine,
facsimile machine, multi-function machine, or generally an
apparatus useful in performing a print process or the like and can
include several marking engines, feed mechanism, scanning assembly
as well as other print media processing units, such as paper
feeders, finishers, and the like. A "printing system" may handle
sheets, webs, substrates, and the like. A printing system can place
marks on any surface, and the like, and is any machine that reads
marks on input sheets; or any combination of such machines.
[0030] The term "fountain solution" or "dampening fluid" refers to
dampening fluid that may coat or cover a surface of a structure
(e.g., imaging member, transfer roll) of an image forming device to
affect connection of a marking material (e.g., ink, toner,
pigmented or dyed particles or fluid) to the surface. The fountain
solution may include water optionally with small amounts of
additives (e.g., isopropyl alcohol, ethanol) added to reduce
surface tension as well as to lower evaporation energy necessary to
support subsequent laser patterning. Low surface energy solvents,
for example volatile silicone oils, can also serve as fountain
solutions. Fountain solutions may also include wetting surfactants,
such as silicone glycol copolymers. The fountain solution may
include D4 or D5 dampening fluid alone, mixed, and/or with wetting
agents. The fountain solution may also include Isopar G, Isopar H,
Dowsil OS20, Dowsil OS30, and mixtures thereof.
[0031] As used herein, the term "opacity" is intended to be a broad
term that means the ability to block the transmission of radiant
energy, e.g., light energy, and less than all or all. Or at least a
substantial portion of the structure and configuration that absorbs
or otherwise blocks light.
[0032] Inking systems or devices may be incorporated into a digital
offset image forming device architecture so that the inking system
is arranged about a central imaging plate, also referred to as an
imaging member. In such a system, the imaging member, including a
central drum or cylinder is provided with a reimageable layer. This
blanket layer has specific properties such as composition, surface
profile, and so on so as to be well suited for receipt and carrying
a layer of a fountain solution. A surface of the imaging member is
reimageable making the imaging member a digital imaging member. The
surface is constructed of elastomeric materials and conformable. A
paper path architecture may be situated adjacent the imaging member
to form a media transfer nip.
[0033] A layer of fountain solution may be applied to the surface
of the imaging member by a dampening system. In a digital
evaporation step, particular portions of the fountain solution
layer applied to the surface of the imaging member may be
evaporated by a digital evaporation system. For example, portions
of the fountain solution layer may be vaporized by an optical
patterning subsystem such as a scanned, modulated laser that
patterns the fluid solution layer to form a latent image. In a
vapor removal step, the vaporized fountain solution may be
collected by a vapor removal device or vacuum to prevent
condensation of the vaporized fountain solution back onto the
imaging plate.
[0034] In an inking step, ink may be transferred from an inking
system to the surface of the imaging member such that the ink
selectively resides in evaporated voids formed by the patterning
subsystem in the fountain solution layer to form an inked image. In
an image transfer step, the inked image is then transferred to a
print substrate such as paper via pressure at the media transfer
nip.
[0035] In a variable lithographic printing process, previously
imaged ink must be removed from the imaging member surface to
prevent ghosting. After an image transfer step, the surface of the
imaging member may be cleaned by a cleaning system so that the
printing process may be repeated. For example, tacky cleaning
rollers may be used to remove residual ink and fountain solution
from the surface of the imaging member. The inking, transferring,
and cleaning process causes the properties of the imaging member or
imaging blanket to undergo wear and tear causing changes through
the life of the blanket. Property changes of the blanket create a
huge variability that makes thin film thickness measurement a
difficult or daunting task.
[0036] FIG. 1 depicts an exemplary ink-based digital image forming
device 10. The image forming device 10 may include dampening
station 12 having fountain solution applicator 14, optical
patterning subsystem 16, inking apparatus 18, and a cleaning device
20. The image forming device 10 may also include one or more
rheological conditioning subsystems 22 as discussed, for example,
in greater detail below. FIG. 1 shows the fountain solution
applicator 14 arranged with a digital imaging member 24 having a
reimageable surface 26. While FIG. 1 shows components that are
formed as rollers, other suitable forms and shapes may be
implemented.
[0037] The imaging member surface 26 may be wear resistant and
flexible. The surface 26 may be reimageable and conformable, having
an elasticity and durometer, and sufficient flexibility for coating
ink over a variety of different media types having different levels
of roughness. A thickness of the reimageable surface layer may be,
for example, about 0.5 millimeters to about 4 millimeters. The
surface 26 should have a weak adhesion force to ink, yet good
oleophilic wetting properties with the ink for promoting uniform
inking of the reimageable surface and subsequent transfer lift of
the ink onto a print substrate.
[0038] The soft, conformable surface 26 of the imaging member 24
may include, for example, hydrophobic polymers such as silicones,
partially or fully fluorinated fluorosilicones and FKM
fluoroelastomers. Other materials may be employed, including blends
of polyurethanes, fluorocarbons, polymer catalysts, platinum
catalyst, hydrosilyation catalyst, etc. The surface may be
configured to conform to a print substrate on which an ink image is
printed. To provide effective wetting of fountain solutions such as
water-based dampening fluid, the silicone surface need not be
hydrophilic, but may be hydrophobic. Wetting surfactants, such as
silicone glycol copolymers, may be added to the fountain solution
to allow the fountain solution to wet the reimageable surface 26.
The imaging member 24 may include conformable reimageable surface
26 of a blanket or belt wrapped around a roll or drum. The imaging
member surface 26 may be temperature controlled to aid in a
printing operation. For example, the imaging member 24 may be
cooled internally (e.g., with chilled fluid) or externally (e.g.,
via a blanket chiller roll 28 to a temperature (e.g., about
10.degree. C.-60.degree. C.) that may aid in the image forming,
transfer and cleaning operations of image forming device 10.
[0039] The reimageable surface 26 or any of the underlying layers
of the reimageable belt/blanket may incorporate a radiation
sensitive filler material that can absorb laser energy or other
highly directed energy in an efficient manner. Examples of suitable
radiation sensitive materials are, for example, microscopic (e.g.,
average particle size less than 10 micrometers) to nanometer sized
(e.g., average particle size less than 1000 nanometers) carbon
black particles, carbon black in the form of nano particles of,
single or multi-wall nanotubes, graphene, iron oxide nano
particles, nickel plated nano particles, etc., added to the polymer
in at least the near-surface region. It is also possible that no
filler material is needed if the wavelength of a laser is chosen so
to match an absorption peak of the molecules contained within the
fountain solution or the molecular chemistry of the outer surface
layer. As an example, a 2.94 .mu.m wavelength laser would be
readily absorbed due to the intrinsic absorption peak of water
molecules at this wavelength.
[0040] The fountain solution applicator 14 may be configured to
deposit a layer of fountain solution onto the imaging member
surface 26 directly or via an intermediate member (e.g., roller 30)
of the dampening station 12. While not being limited to particular
configuration, the fountain solution applicator 14 may include a
series of rollers or sprays (not shown) for uniformly wetting the
reimageable surface 26 with a uniform layer of fountain solution
with the thickness of the layer being controlled. The series of
rollers may be considered as dampening rollers or a dampening unit,
for uniformly wetting the reimageable surface 26 with a layer of
fountain solution. The fountain solution may be applied by fluid or
vapor deposition to create a thin layer (e.g., between about 0.01
.mu.m and about 1.0 .mu.m in thickness, less than 5 .mu.m, about 50
nm to 100 nm) of the fountain solution for uniform wetting and
pinning.
[0041] A sensor 32, for example an in-situ non-contact laser gloss
sensor or laser contrast sensor, may be used to confirm the
uniformity of the layer. Such a sensor can be used to automate the
dampening station 12. While not being limited to a particular
utility, the sensor 32 may provide feedback to control the
deposition of the fountain solution onto reimageable surface
26.
[0042] The optical patterning subsystem 16 is located downstream
the fountain solution applicator 14 in the printing processing
direction to selectively pattern a latent image in the layer of
fountain solution by image-wise patterning using, for example,
laser energy. For example, the fountain solution layer is exposed
to an energy source (e.g. a laser) that selectively applies energy
to portions of the layer to image-wise evaporate the fountain
solution and create a latent "negative" of the ink image that is
desired to be printed on a receiving substrate 34. Image areas are
created where ink is desired, and non-image areas are created where
the fountain solution remains. While the optical patterning
subsystem 16 is shown as including laser emitter 36, it should be
understood that a variety of different systems may be used to
deliver the optical energy to pattern the fountain solution
layer.
[0043] Still referring to FIG. 1, a vapor vacuum 38 or air knife
may be positioned downstream the optical patterning subsystem to
collect vaporized fountain solution and thus avoid leakage of
excess fountain solution into the environment. Reclaiming excess
vapor prevents fountain solution from depositing uncontrollably
prior to the inking apparatus 18 and imaging member 24 interface.
The vapor vacuum 38 may also prevent fountain solution vapor from
entering the environment. Reclaimed fountain solution vapor can be
condensed, filtered and reused as understood by a skilled artisan
to help minimize the overall use of fountain solution by the image
forming device 10.
[0044] Following patterning of the fountain solution layer by the
optical patterning subsystem 16, the patterned layer over the
reimageable surface 26 is presented to the inking apparatus 18. The
inker apparatus 18 is positioned downstream the optical patterning
subsystem 16 to apply a uniform layer of ink over the layer of
fountain solution and the reimageable surface layer 26 of the
imaging member 24. The inking apparatus 18 may deposit the ink to
the evaporated pattern representing the imaged portions of the
reimageable surface 26, while ink deposited on the unformatted
portions of the fountain solution will not adhere based on a
hydrophobic and/or oleophobic nature of those portions. The inking
apparatus may heat the ink before it is applied to the surface 26
to lower the viscosity of the ink for better spreading into imaged
portion pockets of the reimageable surface. For example, one or
more rollers 40 of the inking apparatus 18 may be heated, as well
understood by a skilled artisan. Inking roller 40 is understood to
have a structure for depositing marking material onto the
reimageable surface layer 26, and may include an anilox roller or
an ink nozzle. Excess ink may be metered from the inking roller 40
back to an ink container 42 of the inker apparatus 18 via a
metering member 44 (e.g., doctor blade, air knife).
[0045] Although the marking material may be an ink, such as a
UV-curable ink, the disclosed embodiments are not intended to be
limited to such a construct. The ink may be a UV-curable ink or
another ink that hardens when exposed to UV radiation. The ink may
be another ink having a cohesive bond that increases, for example,
by increasing its viscosity. For example, the ink may be a solvent
ink or aqueous ink that thickens when cooled and thins when
heated.
[0046] Downstream the inking apparatus 18 in the printing process
direction resides ink image transfer station 46 that transfers the
ink image from the imaging member surface 26 to a print substrate
34. The transfer occurs as the substrate 34 is passed through a
transfer nip 48 between the imaging member 24 and an impression
roller 50 such that the ink within the imaged portion pockets of
the reimageable surface 26 is brought into physical contact with
the substrate 34.
[0047] Rheological conditioning subsystems 22 may be used to
increase the viscosity of the ink at specific locations of the
digital offset image forming device 10 as desired. While not being
limited to a particular theory, rheological conditioning subsystem
22 may include a curing mechanism 52, such as a UV curing lamp
(e.g., standard laser, UV laser, high powered UV LED light source),
wavelength tunable photoinitiator, or other UV source, that exposes
the ink to an amount of UV light (e.g., # of photons radiation) to
at least partially cure the ink/coating to a tacky or solid state.
The curing mechanism may include various forms of optical or photo
curing, thermal curing, electron beam curing, drying, or chemical
curing. In the exemplary image forming device 10 depicted in FIG.
1, rheological conditioning subsystem 22 may be positioned adjacent
the substrate 34 downstream the ink image transfer station 46 to
cure the ink image transferred to the substrate. Rheological
conditioning subsystems 22 may also be positioned adjacent the
imaging member surface 26 between the ink image transfer station 46
and cleaning device 20 as a preconditioner to harden any residual
ink 54 for easier removal from the imaging member surface 26 that
prepares the surface to repeat the digital image forming
operation.
[0048] This residual ink removal is most preferably undertaken
without scraping or wearing the imageable surface of the imaging
member. Removal of such remaining fluid residue may be accomplished
through use of some form of cleaning device 20 adjacent the surface
26 between the ink image transfer station 46 and the fountain
solution applicator 14. Such a cleaning device 20 may include at
least a first cleaning member 56 such as a sticky or tacky roller
in physical contact with the imaging member surface 26, with the
sticky or tacky roller removing residual fluid materials (e.g.,
ink, fountain solution) from the surface. The sticky or tacky
roller may then be brought into contact with a smooth roller (not
shown) to which the residual fluids may be transferred from the
sticky or tacky member, the fluids being subsequently stripped from
the smooth roller by, for example, a doctor blade or other like
device and collected as waste. It is understood that the cleaning
device 20 is one of numerous types of cleaning devices and that
other cleaning devices designed to remove residual ink/fountain
solution from the surface of imaging member 24 are considered
within the scope of the embodiments. For example, the cleaning
device could include at least one roller, brush, web, belt, tacky
roller, buffing wheel, etc., as well understood by a skilled
artisan.
[0049] In the image forming device 10, functions and utility
provided by the dampening station 12, optical patterning subsystem
16, inking apparatus 18, cleaning device 20, rheological
conditioning subsystems 22, imaging member 24 and sensor 32 may be
controlled, at least in part by controller 60 components which are
shown and described in FIG. 9 as controller 900. Such a controller
60 is shown in FIG. 1 and may be further designed to receive
information and instructions from a workstation or other image
input devices (e.g., computers, smart phones, laptops, tablets,
kiosk) to coordinate the image formation on the print substrate
through the various subsystems such as the dampening station 12,
patterning subsystem 16, inking apparatus 18, imaging member 24 and
sensor 32 as discussed in greater detail below and understood by a
skilled artisan.
[0050] FIG. 2 shows a schematic view of a clear glass roll with
internal emissive lighting system to illuminate solidified fountain
solution on surface of roller in accordance to an embodiment.
[0051] Components of the fountain measurement system 200 comprise a
transfer roll such as glass roll 210, emissive light 235, light
detector 240, and cooler 220 for changing the phase of the
transferred fountain solution from surface 26 of imaging roll 24.
The transfer roll is specially engineered to a smooth enough
texture as to measure the optical characteristics of the solidified
fountain solution film. In this embodiment the roller would be
transparent with the capability of allowing illumination 235 from
either within or outside the roll associated with a source driver
230 that can change the illumination level of light source 235. The
state of the film of fountain solution on roll 210 alters the
opacity and can be varied by altering the state of the film. The
light source 235 can include one or more light emitting diodes
(LEDs), superluminescent LEDs (SLEDs), lasers, and the like for
transmitting optical radiation (for example, light at one or more
wavelengths) into roller 210 or reflecting off the surface of
roller 210. The system would allow this illumination to be conveyed
through the solidified film of fountain solution to a sensor (i.e.
CCD) that records the light transmitted through. A lower relative
velocity between the imaging blanket 24 and transfer roll can be
used in order to achieve the uniform film on the glass roll
210.
[0052] The fountain solution measurement 200 includes a light
source 235 that illuminates the glass roll 210 with light and a
detector 240 that receives light passing through the glass surface
from the light source and that generates an output signal that
corresponds to receive light. As light passes through the glass
roll 210 the intensity is and proportional to the thickness of the
layer. When fountain solution is introduced on the surface of glass
roll 210 the intensity of the received light at detector 240 is
attenuated. Using the well-known Beer-Lambert law this attenuation
can be expressed as a certain fraction per unit thickness.
[0053] In operation the engineered surface (glass roller) is placed
near the surface 26 of imaging blanket 24, and in Inter-document
zone or any other non-printing area of the imaging blanket, then
using a heat source (LED bar or laser) to evaporate the fountain
solution from the surface 26 of the blanket. The roller w/
engineered surface will be at a temperature significantly cold
enough for complete condensation (Vapor pressure for fountain
solution is approximately 25.degree. C.). Now that a portion or all
the layer of fountain solution has been removed from the blanket
and re-deposited onto the engineered roller surface, a measurement
of the amount of fountain solution on the engineered roller surface
can be obtained.
[0054] Glass roll 210 is rotated 215 at different speeds and
direction as commanded by controller 60. Additionally, the
temperature of glass roll 210 can be maintained or set by
controller 60 using cooler 220 which may be a physical cooling
mechanism, as well as via chemical cooling. Cooler 220 can be
external or internal to the roll and can comprise a Peltier effect
cooling device, a coolant circulated in conduits of a coolant
circulating system, or any other suitable internally-located
cooling mechanism. The glass roller with the engineered transparent
surface would be maintained under conditions below the freezing
point of the fountain solution. For fountain solution such as
Cyclosiloxane, Octamethylcyclotetrasiloxane and the like this is a
temperature lower than 17 Celsius (<17 deg C.). In this state
the fountain solution would have moved from being a liquid to a
solid state. In its solid state the fountain solution crystalizes
and changes opacity with the thickness of the film. One can then
determine concentrated film thickness by opacity or crystallization
measurement on the outer surface of roller 210.
[0055] By continuously monitoring the light 235 as it passes
through the glass roll 210, the change in opacity due to the
introduction of crystallization on the roll can be measured. Using
the captured image the fountain solution thickness can be
determined and controlled.
[0056] FIG. 3 is part of a digital image forming device that
includes a feedback loop for controlling and applicator that
dispenses fluid solution in accordance to an embodiment. Apparatus
comprises an applicator for dispensing fountain solution through
valve actuator 315, an fountain solution measurement with glass
roll 210 and light detector 240, and a controller 60. In operation,
transfer the FS film from blanket surface 26 to a transparent
roller 210 where its depth can be increased and controlled by
concentrating the fountain solution film on the well-controlled
surface. Then the fountain solution on roll 210 is illuminated from
one side to test for levels of opacity due to changes in the
fountain solution solid based on the thickness. As noted above with
reference to FIG. 2 changes in thickness affects the crystal
structure and changes opacity limiting the light transfer through
the fountain solution and transparent roller. By analyzing the
light output to a light detector 240 like a CCD device the film
thickness is determined. Controller 60 evaluates the CCD image for
solid texture to evaluate opacity and thickness via image analysis
i.e. MatLab. Controller 60 produces actionable information such as
control values that can be used by the dampening solution subsystem
such as fountain solution applicator 14 to increase or decrease the
fountain solution applied to imaging blanket 24 or digital imaging
member.
[0057] FIG. 4 is a block diagram of a controller with a processor
for executing instructions to automatically control devices in the
digital image forming device depicted in FIGS. 1-3 in accordance to
an embodiment.
[0058] The controller 60 may be embodied within devices such as a
desktop computer, a laptop computer, a handheld computer, an
embedded processor, a handheld communication device, or another
type of computing device, or the like. The controller 60 may
include a memory 320, a processor 330, input/output devices 340, a
display 330 and a bus 360. The bus 360 may permit communication and
transfer of signals among the components of the computing device
60.
[0059] Processor 330 may include at least one conventional
processor or microprocessor that interprets and executes
instructions. The processor 330 may be a general purpose processor
or a special purpose integrated circuit, such as an ASIC, and may
include more than one processor section. Additionally, the
controller 60 may include a plurality of processors 330.
[0060] Memory 320 may be a random access memory (RAM) or another
type of dynamic storage device that stores information and
instructions for execution by processor 330. Memory 320 may also
include a read-only memory (ROM) which may include a conventional
ROM device or another type of static storage device that stores
static information and instructions for processor 330. The memory
320 may be any memory device that stores data for use by controller
60. Memory 320 maintains a multidimensional lookup table (LUT) of
control values such as values correlating the fountain solution
thickness to opacity or instructions for calculating FS thickness
using Beer-Lambert Law for opacity and thickness. These LUT values
can be used to print a diagnostic print or to make adjustment to
the fountain solution to optimized control values for printing.
[0061] Input/output devices 340 (I/O devices) may include one or
more conventional input mechanisms that permit a user to input
information to the controller 60, such as a microphone, touchpad,
keypad, keyboard, mouse, pen, stylus, voice recognition device,
buttons, and the like, and output mechanisms such as one or more
conventional mechanisms that output information to the user,
including a display, one or more speakers, a storage medium, such
as a memory, magnetic or optical disk, disk drive, a printer
device, and the like, and/or interfaces for the above. The display
330 may typically be an LCD or CRT display as used on many
conventional computing devices, or any other type of display
device.
[0062] The controller 60 may perform functions in response to
processor 330 by executing sequences of instructions or instruction
sets contained in a computer-readable medium, such as, for example,
memory 320. Such instructions may be read into memory 320 from
another computer-readable medium, such as a storage device, or from
a separate device via a communication interface, or may be
downloaded from an external source such as the Internet. The
controller 60 may be a stand-alone controller, such as a personal
computer, or may be connected to a network such as an intranet, the
Internet, and the like. Other elements may be included with the
controller 60 as needed.
[0063] The memory 320 may store instructions that may be executed
by the processor to perform various functions. For example, the
memory may store instructions to control the application of
fountain solution, dithering and controlling the current applied to
the laser so as to adjust the optical power for patterning the
fountain solution on the digital imaging member 24, and other
control functions enumerated herewith.
[0064] FIG. 5 shows transferring fountain solution by evaporation
from the imaging blanket to the clear glass roll for fountain
solution measurement in accordance to an embodiment illustrated is
a method of transferring fountain solution 25 to glass roll 210,
which forms part of the fountain measurement system 200, through
evaporation and re-condensation. After transferring of the fountain
solution measurement system 200 in cooperation with light,
detector, and controller measures the thickness by monitoring the
change of opacity of the glass roll 210.
[0065] The original fountain solution 25 is heated to evaporation
510 in close proximity of the transfer roll/member 210, which is
kept at low temperature. The vapor will quickly re-condense 520 on
the transfer roll surface of 210 where fountain measurement system
200 uses optical properties of solidified fountain solution film to
determine thickness. Subsequent film thickness measurement can be
performed on the glass roll surface using an emissive light,
detector, and controller like shown in FIG. 2. It should be noted,
in this process of evaporation/re-condensation transfer, the
transfer member 210 can operate in either direction. Additionally,
the speed of the transfer member 210 can be significantly different
from that of the original fountain solution carrier like imaging
blanket 24. With variable speed and direction 215 would provide the
opportunity to concentrate/thicken the fountain solution on the
transfer roll 210. For example, one can run the transfer roll at
1/10 the speed of the blanket 24. The fountain solution on the
transfer member 210 will then be much thicker for easier
measurements. Of course, one could also run the transfer roll 210
faster to obtain a thinner film if desired. Being able to thicken
and thin the film during transfer can greatly enhance the dynamic
range of the measurement system.
[0066] FIG. 6 is a plot of opacity as a function of thickness of
the solidified fountain solution in accordance to an embodiment.
Opacity transfer function 600 shows the relationship between
fountain solution thickness 610 as function opacity 620 on a glass
such as glass roll 210. In the plot opacity 620 represents length
of glass--measured in pixels with thickness increasing from left to
right. The transfer function 600 shows a spike 640 created by
clamps which secured the glass structure for testing. The transfer
function is consistent with Beer-Lambert Law and the relationship
of penetration depth that measures how deep light or any
electromagnetic radiation can penetrate fountain solution on the
surface of glass roll 210.
[0067] FIG. 7 is a flowchart depicting the operation of an
exemplary method to directly measure fountain solution for use in a
digital image forming device. Method 700 begins with action 710
when the system or operator invokes a fountain solution measurement
routine at lithography system 10 of FIG. 1. In action 710, method
700 illuminates engineered surface using emissive light source like
described in FIG. 2. In action 720, the method 700 receives light
passing through engineered surface using a light detector. In
action 730, the method 700 generates output signals that correspond
to the opacity level of the engineered surface like shown in FIG.
6. In action 740, method 700 determines fountain solution thickness
(FST) from the opacity level of the engineered surface. Actions 750
and 760 are of importance when image forming 10 is being controlled
to maintain and/or achieve a certain level of fountain solution
thickness. In action 750, method 700 checks to see if the
determined fountain solution thickness is within a certain range.
The range should be between 48 to 52 nanometers (nm) with roughly
estimated thickness around 50 nm to prevent ink from developing in
the background to maintain image quality. If FST is within range
then control is action 710 to continue to monitor the thickness of
the fountain solution. However, if FST is not in range then control
is passed to action 760 where a control signal is send to the
fountain solution deposition process to increase or decrease the
fountain solution by an amount proportional to the deviation from
the range.
[0068] Those skilled in the art will appreciate that other
embodiments of the disclosed subject matter may be practiced with
many types of image forming elements common to offset inking system
in many different configurations. For example, although digital
lithographic systems and methods are shown in the discussed
embodiments, the examples may apply to analog image forming systems
and methods, including analog offset inking systems and methods. It
should be understood that these are non-limiting examples of the
variations that may be undertaken according to the disclosed
schemes. In other words, no particular limiting configuration is to
be implied from the above description and the accompanying
drawings.
[0069] It will be appreciated that various of the above-disclosed
and other features and functions, or alternatives thereof, may be
desirably combined into many other different systems or
applications. Also, various presently unforeseen or unanticipated
alternatives, modifications, variations or improvements therein may
be subsequently made by those skilled in the art.
* * * * *